Molecular phylogeny of shrimps from the genus Lysmata (Caridea: Hippolytidae): the evolutionary origins of protandric simultaneous hermaphroditism and social monogamy

Shrimps from the genus Lysmata are known because of their wide diversity of lifestyles, mating systems, symbiotic partnerships, and conspicuous coloration. They can occur in crowds (large aggregations), in small groups, or as socially monogamous pairs. Shrimps from this genus are rare, if not unique among crustaceans, because of their unusual sexual system. To date, the sexual system of all species investigated comprises a protandric simultaneous hermaphroditism: shrimps initially mature and reproduce as males and later in life turn into functional simultaneous hermaphrodites. The evolutionary relationships of the species within the genus are unsettled. A molecular phylogeny of the group may shed light on the evolutionary origins of the peculiar sexual and social systems of these shrimps and help resolve standing taxonomic questions long overdue. Using a 647-bp alignment of the 16S rRNA mitochondrial DNA, we examined the phylogenetic relationship of 21 species of shrimps from the genus Lysmata from several biogeographical regions; the Atlantic, Pacific, and Indo-Pacific. The resulting phylogeny indicates that the genus is paraphyletic and includes the genus Exhippolysmata . The constituent species are subdivided into three well supported clades: one group exclusively composed of neotropical species; a second clade comprising the Indo-Pacific and Atlantic symbiotic fish cleaner shrimps; and a third clade including tropical and temperate species from the Atlantic and Pacific. The molecular phylogeny presented here does not support a historical contingency hypothesis, previously proposed to explain the origins of protandric simultaneous hermaphroditism within the genus. Furthermore, the present study shows that monogamous pair-living is restricted to one monophyletic group of shrimps and therefore probably evolved only once.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 415–424.     

Genetic and morphological differentiation patterns between sister species: the case of Onthophagus taurus and Onthophagus illyricus (Coleoptera, Scarabaeidae)

The present study investigated the morphological and genetic differentiation pattern between two sympatric dung beetle sister species, Onthophagus taurus and Onthophagus illyricus . The geometric morphometric approach coupled with the use of molecular markers allowed examination of the nature of interspecific relationships and an outline of the evolutionary and geographical processes that might have led to interspecific differentiation and the present-day partial sympatric and syntopic pattern of distribution. Geometric morphometrics failed to discrimininate the two species on the ground of external morphological traits, but revealed interspecific differences when the shape of the primary sexual traits was taken into account. The use of two different molecular markers (cytochrome oxidase subunit I gene and amplified fragment-length polymorphism) demonstrates that the two species are genetically well differentiated, forming two distinguishable lineages probably diverged during the Pliocene by allopatric speciation. No evidence of past or recent introgression and no support for hybridization were found, suggesting that sympatry was established subsequently, when speciation was accomplished. Both molecular markers and genital shape indicate that phenotypically intermediate individuals, despite their ambiguous appearance, are members of O. illyricus species rather than hybrids.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 197–211.     

Shell microstructure of the early bivalve Pojetaia and the independent origin of nacre within the mollusca

Abstract: Pojetaia and Fordilla are the oldest bivalve molluscs, occurring in roughly co‐eval rocks from the Tommotian, and are the only undisputed, well‐known bivalves from the Cambrian. New specimens reveal that Pojetaia had a laminar inner shell microstructure reminiscent of the foliated aragonite of modern monoplacophorans, and the same is true for Fordilla. A similar shell microstructure is seen in Anabarella and Watsonella, providing support for the hypothesis that they are the ancestors of bivalves. Foliated aragonite shares many similarities with nacre, and it may have been the precursor to nacre in bivalves. No cases of undisputed nacre occur in the Cambrian, in spite of much shell microstructure data from molluscs of this time period. Thus, although considered by many to be homologous among molluscs, we conclude that nacre convergently evolved in monoplacophorans, gastropods, bivalves, and cephalopods. This independent origin of nacre appears to have taken place during, or just prior to, the Great Ordovician Biodiversification Event and represents a significant step in the arms race between predators and molluscan prey.     

Does calcium ameliorate the negative effect of NaCl on melon root water transport by regulating aquaporin activity?

The hydraulic conductance ( L ₀) of detached, exuding root systems from melon ( Cucumis melo cv. Amarillo oro) was measured. All plants received a half-strength Hoagland nutrient solution, and plants stressed either solely with NaCl (50 mM) or with NaCl (50 mM) following treatment (2 d) with CaCl₂ (10 mM) were compared with controls and CaCl₂-treated (10 mM) plants. The L ₀ of NaCl-treated plants was markedly decreased when compared to control and CaCl₂-treated plants, but the decrease was smaller when NaCl was added to plants previously treated with CaCl₂. A similar effect was observed when the flux of Ca²⁺ into the xylem and the Ca²⁺ concentration in the plasma membrane of the root cells were determined. In control, CaCl₂- and NaCl + CaCl₂-treated plants, HgCl₂ treatment (50 μM) caused a sharp decline in L ₀ to values similar to those of NaCl-stressed roots, but L ₀ was restored by treatment with 5 mM DTT. However, in NaCl roots only a slight effect of Hg²⁺ and DTT were observed. The effect of all treatments on L ₀ was similar to that on osmotic water permeability ( P _f) of individual protoplasts isolated from roots. The results suggest that NaCl decreased the passage of water through the membrane and roots by reducing the activity of Hg-sensitive water channels. The ameliorative effect of Ca²⁺ on NaCl stress could be related to water-channel function.     

Production and morphology of fruit and seeds in Genisteae (Fabaceae) of south-west Spain

The productivity and morphology of fruit and seeds were studied in 30 species (and subspecies) of the tribe Genisteae (Fabaceae) in south-west Spain. The morphological characters of greatest taxonomic value both for the segregation of the two subtribes (Genistinae and Lupininae) recognized in Genisteae and for the delimitation of the lower taxonomic levels (genus and species) are the size of the pod and characters of the pericarp, the colour and weight of the seeds, whether or not an ad exists, and the shape, size, and position of the hilum. In contrast, characters of little taxonomic interest are pod colour, shape and number of seeds, and characters of the lens. There were also found to be major relationships between fruit and seed, and between these and other floral (e.g. corolla size) or reproductive (e.g. polledovule [P/O] and seed/ovule [S/O] ratios) attributes. Thus in this tribe, pod size was positively correlated with corolla size, seed size, the number of viable seeddfruit, and the S/O and P/O ratios. Corolla size was positively correlated with the number of viable seeds/ fruit and with the seed weight. Similarly, the number of seeddfruit was positively correlated with the fruit's weight and with the number of ovules/ovary. Also, the weight of the seeds was positively correlated with the pollen/ovule ratio. There was also positive correlation between the S/O and P/O ratios.     

Regulation of spiral growth in planorbid gastropods

Extensive experimentation has been performed on the planorbid Planorbarius metidjensis in order to determine which mechanism allows the snail to coil its shell regularly. Individuals of this species, like all Planorbidae, are permanently active and secrete their shells while crawling on the substrate. Experiments consisted of attaching weights to either side of the shell (which is carried almost vertically) in an umbilical position; these weights cause the shell to fall towards the substrate on the loaded side. It can be demonstrated, qualitatively and quantitatively, that during further growth the shell tube deviated initially (i.e. within the first half whorl after loading) towards the loaded side. In a later stage, when the animal is able to re-balance the shell-load complex by muscular activity, the shell tube gradually deviates away from the loaded side. This behaviour is to be expected if, after loading, secretion of the shell continued with the aperture parallel to the substrate and forming a constant angle with the direction of growth. The main implication is that in normal conditions the living posture largely controls the correct coiling of the shell. Minor experiments made with another planorbid species, Gyraulus laevis , confirm these conclusions. The growth pattern of planorbids requires that the snail has constant information on the orientation of the shell with respect to the substrate. This is permitted by the particular physiological ecology of this group, members of which, unlike terrestrial gastropods, are permanently active.     

Herpetomonas roitmani (Fiorini et al., 1989) N. Comb.: A Trypanosomatid with a Bacterium-like Endosymbiont in the Cytoplasm

The trypanosomatid previously described as Crithidia roitmani is characterized here at the ultrastructural and biochemical levels. The data indicates that the parasite belongs to the Herpetomonas genus, and we therefore suggest the flagellate to be denominated as Herpetomonas roitmani n. comb. Cladistic analysis of isoenzyme data generated by eight different enzymes showed that the parasite presented a distinct banding pattern and could be grouped with some Herpetomonas spp., but not with Crithidia spp., used as reference strains. Accordingly, when the parasites were grown for longer periods in Roitman's defined medium, expontaneous differentiation from promastigotes to opisthomastigotes (typical of the Herpetomonas genus) occurred. Transmission electron microscopy revealed the presence of bacterium-like endosymbionts in the cytoplasm of all evolutive forms of the parasite. All morphological alterations characteristic of endosymbiont-bearing trypanosomatids could be observed.